1. Fen Hou 、 Lin X. Cai, University of Waterloo Xuemin Shen, Rutgers University Jianwei Huang, Northwestern University IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 60, NO. 4, MAY 2011 Asynchronous Multichannel MAC Design With Difference-Set-Based Hopping Sequences

2. Outline Introduction Goal Difference-set-based hopping sequence DSMMAC Simulation Conclusion

3. Introduction MAC protocol for Wireless Ad Hoc Networks Single channel MAC protocols Multi-channel MAC protocols

4. Introduction Single Channel MAC protocol Easy to communicate Poor network throughput Long transmission delay Multi-Channel MAC protocol High network throughput Low transmission delay

5. Introduction Most existing multichannel MAC protocols have the performance bottlenecks Global synchronization Rendezvous Common control channel Control phase Complete knowledge of all users’ channel selection strategies

6. Goal This paper proposes a multichannel MAC protocol Difference-set-based channel hopping Asynchronization Multiple parallel rendezvous Less signaling overhead No dedicated control channel

7. Assumptions Totally L equal-bandwidth channels are available. There are 2M nodes in the network Each node is equipped with one half-duplex modem which is able to switch to any channel dynamically.

8. Overview Node A Node B 1234567891011 All users use the same sequence for frequency hopping and channel access Any two nodes to rendezvous with a nonzero probability without global synchronization Hopping to channel 1 Time

9. Difference-set-based hopping sequence Difference Sets the set cycle v the set size k the time number λ Node A v = 7 k = 3 Node A Node B λ=1rendezvous probability = λ/v

10. Difference-set-based hopping sequence (v, k, λ) = (7,3,1) D = {1,2,4} is an example r = (d i - d j ) mod v r ∈ {1,2,3,4,5,6}, each r is smaller than v D = {1,2,5} is not an example (1-2) (1-4) (2-1) (2-4) (4-1) (4-2) mod 7 = 6 mod 7 = 4 mod 7 = 1 mod 7 = 5 mod 7 = 3 mod 7 = 2 (1-2) (1-5) (2-1) (2-5) (5-1) (5-2) mod 7 = 6 mod 7 = 3 mod 7 = 1 mod 7 = 4 mod 7 = 3

11. Difference-set-based hopping sequence D = {1,2,4} Node A Node B (1-2) (1-4) (2-1) (2-4) (4-1) (4-2) mod 7 = 6 mod 7 = 4 mod 7 = 1 mod 7 = 5 mod 7 = 3 mod 7 = 2 1234567 1234567 1234567 1234567 D = {1,2,5} (1-2) (1-5) (2-1) (2-5) (5-1) (5-2) mod 7 = 6 mod 7 = 3 mod 7 = 1 mod 7 = 4 mod 7 = 3 1234567 Node A 1234567 Node B

12. Difference-set-based hopping sequence Nodes A and B follow the same hopping sequence generated from a difference set (11, 5, 2) D = {1,3,4,5,9}

13. Design of the Difference-Set-Based Hopping Sequence (v, k, λ) = (7,3,1) D 1 = {1,2,4} D 2 = {3,5,6,7}

14. Design of the Difference-Set-Based Hopping Sequence Example (v, k, λ) = (73,9,1)

15. Difference-Set-Based Multichannel MAC Design DSMMAC 1121222 1121222 1121222 1121222 1121222 1121222 Node A Node B A B RTS CTS Channel 1 Channel 2 C D RTS 1121222 1121222 1121222 1121222 1121222 1121222 Node C Node D T max CTS

16. Simulation

17. Select at random a permutation of these 3 channels, say the permutation (1, 2, 3)

18. Simulation

20. Conclusion The proposed DSMMAC protocol No need for further information exchange, and no central controller or centralized allocation is needed. Ensures that a source node can successfully meet its destination with a certain probability, even without synchronization. Achieve multiple parallel rendezvous and improves the channel utilization.

21. Thank You